1. Field of the Invention
This invention relates to a method for coating a metal cookware, more particularly to a method for coating a metal cookware having scratch-resistant and anti-stick characteristics and a relatively long service life.
2. Description of Related Arts
The common methods used for surface treatment of metal cookware are described as follows:
1. The cooking surface of the metal cookware is roughened by blasting abrasive particles, such as aluminum oxide (Al.sub.2 O.sub.3) or steel grains, against the cooking surface. A hard oxide film is then formed on the roughened cooking surface by an anodic oxidation. During the anodic oxidation, an electrolytic solution containing sulfuric acid or oxalic acid is employed. Since the hard oxide film is provided on the cooking surface of the metal cookware, the cooking surface has a scratch-resistant characteristic. However, a main drawback of the metal cookware is that the cooking surface does not have an anti-stick characteristic, thereby facilitating the accumulation of greasy dirt thereon.
2. The cooking surface of the metal cookware is roughened by blasting abrasive particles, such as aluminum oxide (Al.sub.2 O.sub.3) or steel grains, against the cooking surface. An anti-stick film is then formed by spraying suspended fluorocarbon resin upon the roughened cooking surface. Since the fluorocarbon resin film is provided on the cooking surface of the metal cookware, the cooking surface has an anti-stick characteristic. However, the hardness of the cooking surface of the metal cookware is relatively poor such that the cooking surface is susceptible to scratching.
3. After the cooking surface is roughened, a hard oxide film is applied on the roughened cooking surface, and an anti-stick film is then applied upon the hard oxide film. Referring to FIG. 1, abrasive particles, such as Al.sub.2 O.sub.3 or steel grains, are blasted against the cooking surface of the metal cookware 6 to form a roughened surface 61. Referring to FIG. 2, a porous hard oxide film 7 is coated on the roughened surface 61 by an anodic oxidation with the use of the electrolytic solution containing sulfuric acid or oxalic acid. Referring to FIG. 3, the hard oxide film 7 of the metal cookware 6 is further coated with an anti-stick film 8. Since the metal cookware 6 is provided with both the hard oxide film 7 and the anti-stick film 8, the cooking surface of the metal cookware 6 has the scratch-resistant and anti-stick characteristics. Referring to FIGS. 2 and 3, the formation of the roughened surface 61 can facilitate the attachment and bonding of the hard oxide film 7 to the metal cookware 6. However, since the roughness of the hard oxide film 7 is relatively low, the attachment and bonding between the hard oxide film 7 and the anti-stick film 8 is not strong. Therefore, the anti-stick film 8 easily peels off after a period of use.